values of cosine in a domain

[khurram]

if f(x)=sin x=>f'(x)=cos x

then how f'(x) is -ve for -PI<x<-PI/2

here PI means symbol Pi which we use to measure radian angles.

I'm also confused about 90 & -90.I know -90 means 270 degree.But what's -180 degree.Is it 0 degree?.[/code][/list]

 

[tkhunny]

if f(x)=sin x=>f'(x)=cos x

then how f'(x) is -ve for -PI<x<-PI/2

here PI means symbol Pi which we use to measure radian angles.

I'm also confused about 90 & -90.I know -90 means 270 degree.But what's -180 degree.Is it 0 degree?.[/code][/list]

There's a ton of stuff going on in here...

"then how f'(x) is -ve" - What does that mean?

"I know -90 means 270 degree" - Then you had better UNknow it, since that is not correct.

"But what's -180 degree.Is it 0 degree?" - Why would that be the case?

You need more background on:

• Inverse Functions
  Trig Functions Defined on the Real Numbers
  Trig Functions Defined on the Unit Circle
  Reference Angles

 

[khurram]

Hello Tkhunnky,

I've been forced to be off my acadamia due to a decade long illness. I've been a brilliant student of Maths.Now I'm refreshing my concepts at my home. Long illness've blurred some even minor concepts from my mind. I want to know what's difference between (- PI & PI or -180 degree & 180 degree.- 90 & 90 etc.). Thanks.

 

[stapel]

The point the tutor was making was that, if you really don't understand the differences, then you almost certainly need more help than we can provide here.

Please consider taking a trigonometry course, or else hiring a tutor local to your area. If you meet with this tutor, working face to face for a few hours a week (daily would be best), you should be able to learn the necessary background information in possibly less than a month.

My best wishes to you.

Eliz.